This is a quotation within a quotation. It can be stated as an indirect quotation. Alternate translation: "tell his disciples that he has risen from the dead and that Jesus has gone ahead of you to Galilee, where you will see him." (See: [[rc://en/ta/man/translate/figs-quotesinquotes]] and [[rc://en/ta/man/translate/figs-quotations]])
From among all those who have died. The expression "the dead" describes all dead people together in the underworld. To rise from among them speaks of becoming alive again.